The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Mounjaro Side Effects — Understanding Cost and Access in the UK
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection that works as a GLP-1 and GIP receptor agonist. Before accessing it in the UK, it's important to understand both potential side effects and the different routes to obtain it — whether through NHS specialist services or private prescription following an online clinical assessment. This guide covers what to expect and how to access this medication.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Mounjaro Side Effects and Private UK Costs
Common side effects reported in clinical trials include nausea, diarrhoea, vomiting, and constipation — typically occurring during dose escalation and often improving over time. These gastrointestinal effects affect more than 1 in 10 people. Less common side effects include injection site reactions, fatigue, dizziness, and hair loss.
- Nausea and vomiting — most common during first 4 weeks on each new dose
- Diarrhoea or constipation — varies between individuals
- Stomach pain — usually mild and transient
- Injection site reactions — redness, bruising at injection site
- Hair loss (alopecia) — reported but reversible
Serious side effects requiring urgent medical attention: severe, persistent abdominal pain (possible pancreatitis), gallbladder problems, serious allergic reactions, or vision changes. These are rare.
Private prescription costs in the UK typically range from £129 to £320 per month depending on the dose you're prescribed — higher doses cost more. Costs vary between private online prescribers and pharmacies.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS vs Private Access — How to Get Mounjaro in the UK
NHS route: Mounjaro is available through NHS tier 3 specialist weight management services, but access is limited and varies significantly by region. Your GP can refer you, though waiting lists can be several months or longer. You'll need a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or hypertension.
Private route: Available through UK-licensed online prescribers and GPhC-registered pharmacies without NHS referral. You complete an online health questionnaire, a prescriber reviews your medical history, and if suitable, a prescription is issued. This typically takes 24–48 hours. The private route offers faster access but at personal cost. Use our free BMI calculator to check your starting point, then discuss options with a prescriber during your online assessment.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
What's the difference between Mounjaro and Wegovy?
Both are weekly weight loss injections licensed in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 receptor agonist only. Clinical trials showed Mounjaro users lost approximately 15–21% of body weight, whilst Wegovy users lost around 15%. Individual results vary significantly and depend on diet, activity, and personal factors.
How much does Mounjaro cost on the NHS?
Mounjaro is free through the NHS if prescribed via specialist tier 3 weight management services, but access varies by region and availability. Many areas have significant waiting lists. Private prescription costs are typically £129–£320 per month depending on your prescribed dose.
What happens if I get serious side effects from Mounjaro?
Seek urgent medical attention if you experience severe, persistent abdominal pain, signs of gallbladder problems, serious allergic reactions (facial swelling, throat tightness), or vision changes. Contact your prescriber immediately or call NHS 111. Most side effects are mild and temporary, improving as your body adjusts to the medication.
Can I switch from Mounjaro to Wegovy if I get side effects?
Possibly, but this must be managed by your prescriber. Some people tolerate one medication better than another. Your prescriber will assess whether switching is appropriate and manage the transition safely. Never stop or switch weight loss medications without medical guidance.
How long does a Mounjaro KwikPen last?
Each KwikPen contains 4 weekly doses, so one pen lasts approximately 4 weeks. You'll need a new pen each month. Storage is crucial — unopened pens must be refrigerated at 2–8°C; opened pens can be kept at room temperature below 30°C for up to 30 days before disposal.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.